In This Issue
Summer Issue of The Bridge on Energy, the Environment, and Climate Change
July 3, 2015 Volume 45 Issue 2

The Future of Biofuel and Food Production in the Context of Climate Change and Emerging Resource Stresses

Monday, July 6, 2015

Author: Chris R. Somerville and Stephen P. Long

Approximately 10 percent of energy use worldwide is derived from direct or indirect combustion of biomass, providing as much energy as hydro, geothermal, solar, and wind combined.

Energy produced by combustion of biomass or biomass-derived compounds is bioenergy, of which liquid biofuels are a small subset. In 2013 some 110 billion liters of biofuels were produced worldwide. About two thirds of the volume was ethanol produced by fermentation of sugars from corn and sugarcane, and one third was biodiesel, mostly fatty acid esters from vegetable oils (IEA 2015).

Approximately 21 million hectares (Mha) of land were used for production of biofuels in 2010 (Langeveld et al. 2014), about 1.4 percent of the 1.5 billion Ha currently used for crop production. Most of the biofuels were produced in the United States and Brazil, but 60 other countries have implemented biofuel mandates or goals (Lane 2013). The projected expansion of biofuel production at 2.7 percent per year from 2010 to 2040 (EIA 2014) implies an increase in the amount of land allocated to them rather than to food, feed, or ecosystem services. Given estimated population growth and possible threats to biodiversity and ecosystems, some believe that public support for the use of biofuels is misguided. At the same time, concern about climate change has stimulated interest in the development and deployment of technologies for biofuel production to reduce net carbon emissions from the use of liquid transportation fuels.

We outline some of the issues that frame the public discourse of these subjects and offer a view of the possible trajectory of biofuels. We focus largely on the United States and Brazil, which currently have the most experience, production, and use.

Corn Ethanol

In 2006–2010 about 30 percent of the US corn crop was used for ethanol production (table 1). About two thirds of the mass of corn kernels is starch, which is depolymerized to sugar and fermented to ethanol; the remaining third, a nutritious high-protein residue termed distillers dried grains, is fed to animals. Most of the corn ethanol produced in the United States is mixed with gasoline to produce a 10 percent blend; small amounts are used to produce 85 percent blends or exported. 

Table 1 

The amount of corn used for ethanol rose significantly during the past 15 years, as did the amount used for other purposes, including exports (table 1).1 The rise in US corn production was due to three factors: (1) higher yield per acre, (2) unused land brought into production, and (3) the transition by some farmers away from less profitable crops. The small expansion (16.3 percent) in land area since the introduction of corn ethanol (table 1) is less than one quarter of the 17 Mha that have dropped out of overall US crop production since 1980 (figure 1; World Bank 2015), and even with the increase, the amount of US land in corn today is about 10 percent less than in 1930.

Figure 1

Since the 1930s average US corn yield has risen about eightfold as a result of improved breeding methods, development of hybrid varieties, greater inputs of chemicals and fertilizers, and improved agronomy, including increased planting density. The higher yield per hectare has been achieved without an increase in the amount of nitrogen fertilizer, which has remained at 140 kg/ha−1 since the 1980s (Long et al. 2015a).

The rise in grain yield has been accompanied by increased production of crop residues and widespread adoption of minimum till agriculture, which may be beginning to cause reaccumulation of carbon in Corn Belt soils after years of decline (Bernacchi et al. 2005). But because the ratio of energy output to input for corn ethanol is about 1.6, net greenhouse gas (GHG) emissions are reduced 34–44 percent compared to those of petroleum-based fuels (Wang et al. 2012). The fermentation process produces nearly pure carbon dioxide (CO2) that could be used directly for geological sequestration, resulting in a CO2-negative or near-negative fuel (IPCC 2014).

Sugarcane Ethanol

The US Environmental Protection Agency classifies sugarcane ethanol as an “advanced biofuel” because of its greater than 50 percent net GHG reduction relative to gasoline. Brazilian sugarcane is the second largest source of ethanol (Youngs et al. 2015): Brazil grows approximately 9 Mha of sugarcane, of which roughly half is used to produce about one third of the world’s sugar and the other half ethanol. Mills burn the bagasse, the solids that remain after extraction of the sugar, to produce energy for processing the sugarcane, and any surplus is exported as electricity to the grid. This bioelectricity production complements the use of hydro, which provides about 70 percent of Brazilian power.

Sugarcane ethanol has a high ratio of net energy capture and contributes to an 82 percent reduction in GHG emissions (Wang et al. 2012). Continued innovation—from crop production to processing of the wastes—promises to further reduce such emissions.

Brazil mandates that gasoline contain 27 percent ethanol, and pure dehydrated ethanol is also sold to retail consumers. Thus ethanol provides about 40 percent of the transportation fuel for the light-duty fleet, which is about 95 percent flexfuel and can use any mix of alcohol and gasoline. Gasoline is subsidized but ethanol is not; consumers purchase the gasoline:ethanol mixture or pure ethanol depending on the relative prices of gasoline and ethanol.

Most sugarcane ethanol is produced in the state of São Paulo, but expansion is planned for adjacent states in a low-productivity region called the Cerrado, which supports about 160 Mha of cattle ranching at very low stocking density. Sugarcane farming will likely expand through intensification of cattle ranching as the demand for biofuels increases (Somerville et al. 2010).

The Brazilian government estimates that as many as 64 Mha of land are suitable for sugarcane production without any negative impact on the Amazon forest or Pantanal regions. Such an expansion might enable Brazil to produce about 15 percent of the volume of liquid fuels that were consumed worldwide in 2014 (IEA 2015; Somerville et al. 2010).

Cellulosic Biofuels

Approximately 70 percent of the body of a plant is a composite of structural polysaccharides, mainly cellulose and hemicellulose, which can be depolymerized with acids or enzymes to glucose or a mixture of sugars, respectively (Youngs and Somerville 2012). The remaining mass is mostly a polyphenolic material called lignin, with small amounts of protein, lipid, and minerals. The sugars that constitute the structural polysaccharides can be fermented by various organisms to produce fuels such as ethanol, termed cellulosic fuels.

The industrial yeasts that have traditionally catalyzed most ethanol production processes are fastidious and use only glucose. Recently, strains have been engineered to use the most abundant sugars derived from hemicellulose with high efficiency, and in 2013–2014 half a dozen small commercial-scale “cellulosic ethanol” biorefineries started operating in Brazil, Europe, and the United States (Youngs et al. 2015), using agricultural residues such as corn stover, wheat straw, and sugarcane bagasse as feedstocks. Residues from forestry operations are also suitable feedstocks for cellulosic fuel production. In all cases care must be taken to ensure that sufficient residue is left on the land to maintain soil carbon contents. Importantly, these cellulosic sources do not compete with resources needed for food production.

Advantages of Cellulosic Biofuels

The whole plant is used rather than just the fruits or tubers, maximizing efficiency of conversion of solar energy into fuels. In addition, feedstocks can be chosen on the basis of high productivity, low input requirements, and the ability to use land unsuited to the production of food crops. A recent survey identifies a number of highly sustainable perennial feedstocks for cellulosic fuels that could be grown on a wide range of lands, including semidesert and salinated soils where no food crops could be grown (Davis et al. 2014a).

Highly productive perennial grasses that produce soil-binding root mats can be grown on land that would be eroded by cultivation for annual food crops. They can also grow on soils too poor for the cultivation of food crops as they recycle mineral nutrients. One such candidate, Miscanthus × giganteus, showed no significant difference in yield when grown on high-quality or marginal land in Illinois (Arundale et al. 2013), and in England it was grown for 14 years without fertilizer, with no evidence of yield loss (Christian et al. 2008).

Perennial growth provides many advantages, including no replanting costs, faster spring emergence resulting in increased solar energy capture, recycling of nutrients, and the capacity to bind the soil with a year-round root and rhizome mat (Davis et al. 2014a; Heaton et al. 2008). Indeed, such crops could bring back into use the millions of US hectares abandoned from row crop use during the Dust Bowl in the 1930s. They can convert more sunlight energy into biomass energy per unit land area than food crops and require lower inputs (Dohleman and Long 2008). Furthermore, analysis suggests that, for the most productive of these species, such as Miscanthus (figure 2), increased soil carbon storage would completely offset the small amount of fossil fuel energy needed over their lifecycle (Dohleman et al. 2012; Wang et al. 2012).

Figure 2 

Production Opportunities and Costs

For the United States, with a large underused land base, especially in the South, there is an opportunity to replace a significant portion of the country’s liquid fuel use with cellulosic fuels without competing with food and feed crops (Davis et al. 2012, 2014a; DOE 2006; Heaton et al. 2008; Miguez et al. 2009; Somerville et al. 2010).

For example, the eastern US ecoregion, which receives sufficient rainfall to support bioenergy crops without irrigation, comprises 165 Mha, about 17 percent of the total area of the 48 contiguous states. But the entire region has been in agricultural decline since the settlement of the Midwest and the Civil War, such that today only 20 percent is in agriculture. This decline is ongoing: between 1986 and 2000, 12 Mha dropped out of row crop production (Loveland and Acevedo 2014)—enough land to support a major replacement of fossil fuel oil use. The use of this land for bioenergy crops could generate a perpetual source of liquid fuels that would offset a major portion of national GHG emissions or, combined with carbon capture and storage, even achieve net removal of carbon from the atmosphere while producing fuel.

The capital costs of lignocellulosic biorefineries are high relative to the value of the fuels produced, but will likely decline as the industry learns by doing. In the meantime, a potentially better option, especially for emerging economies, may be to convert lignocellulosic biomass to methane using anaerobic digesters, which are inexpensive to build and can use essentially any source of organic material. The gas can be used directly to generate electricity in inexpensive and robust reciprocating engine generators or cleaned and compressed for use as transportation fuel in suitably equipped vehicles (Bond and Templeton 2011).

Biodiesel

Ethanol is generally not a suitable fuel for diesel or jet engines, so an industry has developed around the use of fatty acid methyl esters, or derivatives, as “biodiesel.”

Approximately 26 billion liters of biodiesel were produced in 2013 (BP 2014), most from triacylglycerol (TAG) produced as storage oils by plants such as rapeseed, soybean, sunflower, and oil palm. The conversion of such lipids to fuels is simple and inexpensive to implement at any desired scale. Using more advanced conversion methods, known as hydrotreatment, jet fuels may be produced from TAGs (Serrano-Ruiz et al. 2012). However, with the exception of oil palm, the volume produced per hectare and the net energy return are small compared to corn and especially sugarcane ethanol.

Furthermore, all the lipid production in the world would meet only about 20 percent of diesel use, so biodiesel will not scale to a significant fraction of total demand. Therefore, we anticipate that biodiesel production will decline as technologies emerge for converting lignocellulose to liquid fuels that are similar to diesel and jet (Youngs et al. 2015).

Recent breakthroughs in engineering the accumulation of TAG in vegetative tissues of plants (Winichayakul et al. 2013) may open the way to convert highly productive plants such as sugarcane and sweet sorghum into more productive oil crops. Although biodiesel production from algae has received much attention, detailed system evaluations continue to yield costs in excess of $3 per liter even when assuming high pond productivities, which have yet to be substantiated on an annual basis (Long et al. 2015a; Quinn and Davis 2015; Sun et al. 2011).

Land Competition

A recent analysis of 80 studies suggests that bioenergy production could reach 20 percent of all energy use, which is equivalent to the total energy used today in transportation (Slade et al. 2014). While estimates vary greatly, depending on assumptions, the key point is that biofuels will compete with other land uses. This has generated concern that biofuels will displace food production or seminatural ecosystems. 

Most proponents of cellulosic biofuels generally place a high value on food security and ecosystem conservation and share concerns about competing land use, but consider climate change a larger threat to food production and the environment than biofuels because it is not possible to control which hectares are affected by climate change whereas humans can decide which hectares are allocated to biofuels. If biofuels reduce GHG emissions, it will be worthwhile to allocate some land to achieve that benefit, especially if combined with carbon capture and storage (IPCC 2014).

Moreover, a significant amount of land that is not used for food production, or is used very inefficiently, could be used for perennial biofuel feedstocks. For land that has fallen out of row crop production, the planting of productive perennials, such as Miscanthus or switchgrass, would add positive ecosystem services; for example, their productive root systems would protect against erosion and add more soil carbon than if the land were simply left, grazed, or planted to trees (Dohleman et al. 2012).

Studies of historical land use have found that more than 500 million hectares of previously farmed land have been abandoned (Cai et al. 2010; Campbell et al. 2008). Such abandoned land is usually of poor quality, making it attractive for biofuel feedstock production. Lignocellulosic fuels can be made from essentially any plant species, including those adapted to growth on marginal lands, without the need for large inputs of fertilizer, energy, water, or agrichemicals (Davis et al. 2014a). In addition, approximately one quarter of the terrestrial surface is used for grazing. Is that really the best use of so much land?

Food versus Fuel

In many regions of the world, food production is not limited by a lack of arable land but rather by the exclusion—through price support systems, lack of demand, and most notably the European Economic Community (EEC) 1988 set-aside scheme (Regulation (EEC) 1272/88)—of globally significant amounts of land that could be used for food production. Indeed, total crop acreage in the United States has been on a long-term downward trend—from 102 Mha in 1990 to 96 Mha in 2015—partly because of payments to farmers to enroll land for nonproduction under the USDA Conservation Reserve Program and partly because of abandonment of nonprofitable land use (Loveland and Acevedo 2014; USDA 2013).

In the food versus fuel debate, real concerns are less about the availability of food and more about the price of food and feed. Economic theory predicts that any increase in demand increases price. Economic analyses of the effects of biofuel on food prices indicate that biofuels made from food and feed crops do increase the price of food, but estimates of the magnitude of the effect vary widely (Condon et al. 2015).

Averaged across 29 economic models, production of an additional 4 billion liters of corn ethanol in the United States would increase the price of corn by about 2.5 percent. Because the price of grains is a very small portion of retail food prices in developed countries, such small increases have an insignificant effect on consumers. But in regions with large numbers of urban people who live on a few dollars a day and depend on raw grains, such increases may have significant effects. Thus an argument can be made that biofuels harm the most vulnerable people in the world (Wright 2011). On the other hand, rural small farmers who are among the poorest people in developing countries benefit from higher prices, which provide economic incentives for them to invest in increasing production (Achterbosch et al. 2013; Tyner 2013; World Bank 2008).

Farmers should not bear the cost of feeding the world’s poor but should be free to sell to the highest bidder, as with most other producers of goods. It is the responsibility of the larger society to ensure food security for the poor. And it is surely the role of governments to purchase food and provide it to the poor, or provide the infrastructure to improve production through research and extension support to ensure supply, and not impede market mechanisms to try to drive down the prices that farmers can get.

In regions where social equity does not exist or where wealthy elites control a disproportionate share of the land, acreage could, in principle, be directed to the production of biofuel for trade on world markets at the expense of food production. A partial solution to such a scenario is to establish enforceable standards for sustainability and social equity that assure prospective biofuel-importing countries that biofuel production was carried out under acceptable conditions (Achterbosch et al. 2013). Several organizations, such as the Roundtable on Sustainable Biomaterials, have emerged to manage such certification.

Finally, it is important to recognize that biofuels can increase food security by creating a buffer of plant growth that can be repurposed from biofuel to food uses during a crop failure (Wright 2011). Indeed, the biofuel mandates associated with the US Renewable Fuel Standard legislation have such a provision.

In summary, biogas or biodiesel can be simply produced and can increase quality of life in rural locations in poorer countries where access to markets is impaired by distance, poor roads, and lack of transport infrastructure. In such locations food may be produced inexpensively, while petroleum products trade at severalfold the prices in urban areas and electricity supply may be nonexistent. In these areas local biofuel production can provide energy for pumping water, lighting, communications, and refrigeration (Achterbosch et al. 2013; Souza et al. 2015).

Looking Forward

Several large trends loom over the future: Global population will expand, especially in cities, and the climate will continue to change (Long et al. 2015b). Changing diets associated with urbanization will increase demand for food and feed. Climate change will affect agricultural productivity and will almost certainly increase pressure on many ecosystems and the services that they provide (IPCC 2014).

Against this backdrop, it is fair to ask whether biofuels can have a positive effect rather than making matters worse by exacerbating pressure on land use.

One answer is that in a perfect market economy advanced biofuels and sugarcane ethanol may be important sources of liquid fuels as they become less expensive than GHG-emitting liquid fuels that are subject to carbon taxes that fairly account for environmental damages. And, as truly renewable fuels, they offer energy security far into the future. By contrast, corn-based biofuels may gradually disappear because of the relatively low level of net GHG savings and the higher demand for grain associated with population growth (Long et al. 2015b).

As noted earlier, it is impossible to know how much biofuel will be produced in the future because the many assumptions underlying the models cannot be agreed upon, but the International Energy Agency estimates that bioenergy will provide about 27 percent of total human energy use by 2050 (IEA 2011). It is conceivable that bioenergy use, which today is primarily combustion of solids, could evolve to greater use of liquid or gaseous biofuels. Sustained public and private support for continued technical improvements, together with effective and enabling policies, are required to fully realize the potential of bioenergy.

The probable impact of climate change on the availability of land for food, feed, and biofuel production is speculative because of the dependency of such predictions on (1) climate models that yield very varied regional predictions of future temperatures and soil moisture, and (2) crop models that, even for a single future climate scenario, give wildly different projections (Bassu et al. 2014; Li et al. 2015).

Despite this inability to be exact about the future, it seems likely that, because of changes to rainfall patterns and episodes of high temperature and extreme weather, many regions will experience reduced productivity compared to today (IPCC 2014). On the other hand, some regions such as the Canadian prairies will experience higher numbers of frost-free days—i.e., a longer growing season—that may increase agricultural productivity. However, secondary effects, such as expanded ranges of pests and pathogens, will almost certainly be a negative factor.

In view of the implications of population growth and climate change there has recently been more interest in adapting agriculture to marginal growing conditions. Decades of research on drought, salt, and cold tolerance show that there is some scope for genetic selection or modification of agricultural species to growth under conditions that do not support currently used cultivars. It may also be possible to adapt species that naturally survive marginal conditions so that they provide useful products. In particular, species such as agave, which use a type of photosynthesis called crassulacean acid metabolism, have very high drought tolerance and low rates of transpiration compared to other types of plants (Davis et al. 2014b; Somerville et al. 2010). The use of these species for biofuel production and other purposes could open up billions of hectares not suitable for other types of crops.

Overall it appears likely that food-based biofuels, other than sugarcane, will gradually be displaced by advanced biofuels that will significantly contribute to the goal of reducing GHG emissions associated with transportation. Although such fuels will probably not scale to a complete solution for decarbonizing the energy used in transport, they have the potential to be a major part of the solution.

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FOOTNOTES

1 Demand has stalled since 2014 because less than 8 percent of US light-duty vehicles (~19 million) are certified to use more than 10 percent ethanol, so retail distribution outlets are generally unwilling to distribute higher blend

 

About the Author:Chris R. Somerville is the Philomathia Professor of Alternative Energy at the University of California, Berkeley. Stephen P. Long holds the Gutgsell Endowed Chair of Plant Biology and Crop Sciences at the University of Illinois and is director of the Gates Foundation project on Realizing Improved Photosynthetic Efficiency.